Refrigerant choice in HVAC chillers
Climalife UK
In light of the worldwide phase-down of high GWP refrigerants, Dave Richards, UK Head of Sales looks at the various options available for HVAC chillers.
Chillers play a vital role in the Heating, Ventilation, Air Conditioning (HVAC) industry. They have become an essential part of a whole range of commercial facilities such as offices, hotels, restaurants, and hospitals . Most commercial buildings nowadays, use HVAC systems as a means to cool and dehumidify the building and similar to other areas of the industry, there is a growing need for these systems to be both efficient and sustainable.
There are many different types of chiller, however in terms of refrigerant they can be split into three types based on the pressure of the refrigerant. As always legislation is driving and influencing the choice of refrigerant. The F-Gas legislation has not implemented any bans for chiller applications as they have not used refrigerant with a GWP>2500, but the F-Gas phase down steps will have a profound effect on the choice of refrigerant used in new chillers in the next few years. With the next phase down step due in 2024, chiller manufacturers are already moving to lower GWP refrigerants.
Low Pressure Refrigerant Chillers
Historically these originally used CFC R-11 which was replaced by the B1 safety class HCFC R-123, but legislation meant this type of chiller declined in use, although non-ozone depleting R-245fa was used in some equipment. More recently these low pressure chillers have started to make a comeback with the use of very low GWP R-1233zd (GWP = 4.5), an A1 safety class single component refrigerant and R-514A (GWP = 7), an azeotropic B1 safety class refrigerant blend.
Medium Pressure Chillers
This sector has been dominated by R-134a since it was introduced back in the early 1990’s as a replacement for the CFC R-12. R-134a has been used extensively in chiller applications, mainly in larger end of the chiller market with equipment manufacturers still offering a range of equipment with R-134a as the primary option.
Whilst R-134a has a GWP of 1430 and isn’t subject to any current bans in the EU, there are already lower GWP alternatives readily available. Many of the leading manufacturers of chillers produce a range of air cooled, water cooled and remote condenser chillers that have a wide range of cooling capacities from 20kW up to 2MW most now have options designed for use with the refrigerants mentioned below.
R-513A has a GWP of 631, is non-flammable, has been quickly adopted by a number of manufacturers and can easily be used for retrofitting R-134a systems, with very similar cooling capacity and performance. The GWP of R-513A is less than half of the GWP of R-134a which effectively means that twice as much becomes available compared to R-134a in terms of the F-Gas phase-down.
R-1234ze is a single component HFO with a very low GWP (7) making it a very sustainable long-term refrigerant. It has been available since 2012 and has been used in chiller applications where R-134a was previously used, but is not suitable as a retrofit option for R-134a due to a lower cooling capacity. The positives of using R-1234ze are the good energy efficiency, better than R-134a, and even though it is classed as A2L under the ASHRAE 34 and ISO 817 standards, since it is non-flammable below 30°C, for transportation (ADR) and manufacturing (PED) purposes it can be treated as non-flammable.
R-515B was new to the market in 2020, it can be best described as an A1 (non-flammable) version of R-1234ze with almost identical performance characteristics. It has a GWP of 293 and is for use in new equipment. It is not a retrofit option for R-134a as the capacity difference is too great for most applications.
R-1234yf is already in widespread use in the automotive sector and is another single component HFO with a very low GWP (4) and therefore can be considered a long-term sustainable refrigerant. Some chiller options are available for use with R-1234yf which in terms of performance is very close to R-134a. It is an A2L lower flammable classified refrigerant ideally suited for use in new equipment. Under the Pressure Equipment Directive (PED) R-1234yf is in fluid safety group 1. Although retrofitting from R-134a may be possible, any changes to the equipment PED classification need to be thoroughly considered as well as charge size restrictions from EN 378 and a suitable risk assessment will be required, which takes into account any possibility of the formation of flammable zones.
Neither R-1234ze nor R-1234yf come under the F-gas phase-down meaning they provide an unrestricted solution as the phase-down tightens on higher GWP refrigerants in the years ahead.
High Pressure Chillers
Over the last 15 years the use of R-410A in chillers has grown significantly, however with a GWP of 2088, it is not sustainable in new equipment as the F-Gas phase down steps impact. The leading contenders are currently R-454B and R-32, all of which are A2L classified refrigerants. Although some are looking at the options of the medium pressure refrigerants mentioned above.
R-454B with a GWP of 466 appears to be currently leading the way with a number of manufacturers as it is a close match to R-410A in terms of operating performance and properties and has the lowest GWP. We are seeing an increasing number of chiller manufacturers making this option available to the market.
R-32 with a GWP of 675 has seen rapid growth as a replacement for R-410A in split AC systems and we are now starting to see some chillers coming to market with R-32. The properties of R-32 has meant that more equipment re-design may be required by equipment manufacturers.
Other Refrigerants worthy of a mention are R-290 (propane) and R-717 (ammonia). Some manufacturers are offering HVAC systems using R-290 but the requirements for using an A3 highly flammable refrigerant can be a little more restrictive than using a lower or non flammable option. Whilst EN 378 does not restrict charge sizes if the system is in the open air, suitable risk assessment taking into account the potential formation of flammable zones is required and likely to be significantly more restrictive than using a lower flammability option.
The use of R-717 is widespread in industrial chillers where the toxicity and flammability can be more easily managed but is rarely seen for general HVAC applications.
The uptake of flammable refrigerant in some countries is affected by building regulations, but chillers are often roof top mounted, making the use of the low GWP A2L refrigerants a little easier.
Looking to the future
Changing the refrigerant used in chillers is not always a quick process as it must meet a range of criteria, such as operating at the desired pressure and temperature, provide the correct levels of cooling and be more energy efficient than its predecessors. New chillers installed now need to be viable over their lifetime, which can be 20-30 years, so it’s important to choose a chiller that uses a sustainable refrigerant. The chiller manufacturers are moving quickly in the right direction and already have a number of low GWP options available to them to be able to meet the restrictions F‑Gas legislation creates.
There are many leading manufacturers that have released or are releasing equipment that is high performing, energy efficient and cost effective with the use of low GWP refrigerants These offer a long-term solution in order to future proof a buildings air conditioning system and to take steps towards tackling the pressing issue of climate change.
